Objectives To compare compression pressure (CP) of 6.5mm Acutrak Plus (AP) and 4.5mm AO cortical screws (AO) when placed in simulated lateral condylar fractures of variable thickness in cadaveric equine third metacarpal (MC3) bones, and to compare pullout force and strength of AP and AO screws when placed in a synthetic bone substitute.
Results The AO screw configurations generated significantly greater compressive pressure compared to the AP configurations. The ratio of mean CP for AP screws to AO screws at 20, 12, and 8-mm, were 21.6%, 26.2%, and 34.2% respectively. For the pullout study, the AP constructs generated a significantly higher pullout force and strength (60% greater) when compared to the AO constructs.
Conclusion Mean CP for AP screw fixations are weaker than those for AO screw fixations, most notably with the 20 mm fragments. The 12- and 8-mm groups have comparatively better compression characteristics than the 20-mm group, however they are still significantly weaker than the AO fixations. Pullout characteristics for AP screws were expected however dont correlate with compressions characteristics based mainly on screw thread design.
Clinical Relevance Given that the primary goals of surgical repair are to achieve rigid fixation, primary bone healing, and good articular alignment, based on these results, it is recommended that caution should be used when choosing the AP screw for repair of lateral condylar fractures, especially complete fractures. Since interfragmentary compression plays a factor in the overall stability of a repair, it is recommended for use only in patients with thin lateral condyle fracture fragments, as the compression tends to decrease with an increase in thickness. Typically, pullout and compression characteristics are directly proportional for many compression screws, but based on screw thread design, most notably the thread pitch and angulation, greater pullout characteristics are expected with the AP screw without the concurrent increased compressive force and strength. Further works needs to be performed including single cycle to failure and cyclic fatigue testing prior to use in clinical cases.